Structural-scale modeling of the active confinement effect in the steel-concrete bond for reinforced concrete structures

A numerical model to take into account the effect of the stress state on the bond behavior between steel and concrete in reinforced concrete structures is proposed. It is based on a zero thickness element, adapted to large-scale simulations and the use of 1D elements for steel bars. The proposed model also assumes the definition of a bond stress - slip law which includes the confining pressure around the steel bar as a parameter. The implementation of the model is presented and the calibration of the bond law is discussed. A general equation is especially proposed. This evolution law is validated through the comparison to 28 pullout tests. The model is able to reproduce the evolution of the bond stress (especially the bond strength) as a function of the confinement pressure, whatever the configuration (different concrete cover to steel diameter ratios). Finally, the effects at the structural level are investigated on a reinforced concrete fie. The response for different confining pressures is especially studied. It shows the capability of the model to reproduce the "expected" tendencies with an increase of the initial elastic stiffness with increasing pressures and consequently a higher number of cracks in the stabilized nonlinear regime. The "transfer length" is also shown to decrease with increasing confining pressures.